Senior Unsecured Notes and Secured Debt (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Secured debt principal activity
Secured debt issued	$ 109,503,000	$ 89,208,000	$ 157,418,000
Secured debt extinguished	341,839,000	674,103,000	406,210,000
Secured Debt [Member]
Secured debt principal activity
Secured debt principal balance	2,941,765,000	3,010,711,000	2,311,586,000	2,108,384,000
Secured debt issued	109,503,000	89,208,000	157,418,000
Secured debt assumed	204,949,000	1,290,858,000	444,744,000
Secured debt extinguished	(279,559,000)	(614,375,000)	(360,403,000)
Secured debt foreign currency	(41,559,000)	(10,361,000)	187,000
Secured debt principal payments	$ (62,280,000)	$ (56,205,000)	$ (38,744,000)
Secured debt principal balance average rate	0.0494	0.05095	0.0514	0.05285
Secured debt principal issued average rate	0.03374	0.04982	0.04212
Secured debt principal assumed average rate	0.0475	0.04159	0.05681
Secured debt principal extinguished average rate	0.04824	0.0373	0.04672
Secured debt principal foreign currency average rate	0.03811	0.04013	0.05637
Secured debt principal payment average rate	0.0493	0.05248	0.05456